KVM: lapic: do not scan IRR when delivering an interrupt

On interrupt delivery the PPR can only grow (except for auto-EOI),
so it is impossible that non-auto-EOI interrupt delivery results
in KVM_REQ_EVENT.  We can therefore use __apic_update_ppr.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 15 insertions, 4 deletions

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 457fb206647d..10a745faa659 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2115,6 +2115,7 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
 {
         int vector = kvm_apic_has_interrupt(vcpu);
         struct kvm_lapic *apic = vcpu->arch.apic;
+        u32 ppr;
 
         if (vector == -1)
                 return -1;
@@ -2126,13 +2127,23 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
          * because the process would deliver it through the IDT.
          */
 
-        apic_set_isr(vector, apic);
-        apic_update_ppr(apic);
         apic_clear_irr(vector, apic);
-
         if (test_bit(vector, vcpu_to_synic(vcpu)->auto_eoi_bitmap)) {
-                apic_clear_isr(vector, apic);
+                /*
+                 * For auto-EOI interrupts, there might be another pending
+                 * interrupt above PPR, so check whether to raise another
+                 * KVM_REQ_EVENT.
+                 */
                 apic_update_ppr(apic);
+        } else {
+                /*
+                 * For normal interrupts, PPR has been raised and there cannot
+                 * be a higher-priority pending interrupt---except if there was
+                 * a concurrent interrupt injection, but that would have
+                 * triggered KVM_REQ_EVENT already.
+                 */
+                apic_set_isr(vector, apic);
+                __apic_update_ppr(apic, &ppr);
         }
 
         return vector;